Conventionally, as an optical connecting structure that connects an optical fiber and an optical member, a package for an optical waveguide substrate, which can pack an optical waveguide and an optical fiber together, has been used (See references 1 and 2 below). The package disclosed in the reference 1 has a structure in which a groove having a V-shape for aligning the optical fiber at a lower part of the package and a convex part having a V-shape for pressing the optical fiber at an upper part of the package, are arranged. When assembling this package, the optical waveguide substrate is aligned at the lower part of the package, and by aligning the optical fiber at the groove of a lower part of the package, the optical waveguide substrate and the optical fiber are aligned with each other. Subsequently, the optical fiber is arranged between the groove at the lower part of the package and the convex part at the upper part of the package to fix itself. Furthermore, the reference 2 discloses a metallic package in which resin is filled therein. In this package, breaking of the optical fiber by a tension acts on the optical fiber fixed on the optical waveguide substrate, and reduction of adhering characteristics of the adhesive by surrounding moisture can be controlled.
However, although assembling of the package is relatively easy in the reference 1, it is necessary that an optical element such as the optical waveguide substrate installed in the lower part of the package be aligned to the V-shaped groove of the lower part of the package with high accuracy (within about ±1 μm). Therefore, it is desirable that a packaging apparatus be used; however, such packaging apparatuses are very expensive, in practice about ¥20,000,000 to ¥30,000,000. In addition, since the optical fiber is fixed by pressing the optical fiber around an edge part of the package, breaking may easily occur at that position. Furthermore, in the package disclosed in the reference 2, it is difficult to align the optical waveguide substrate in the package.
It is known that accurate aligning of the optical axis of the optical fiber along the vertical direction can be performed by arranging the optical fiber along an optical fiber holding groove. It should be noted that, hereinafter, the upper-lower direction of the vertical direction of the optical axis, that is, a direction to the bottom of the optical fiber holding groove is defined as the y direction, the left-right direction is defined as the x direction, and the axis direction of the optical axis is defined as the z direction. As the optical fiber holding groove, a structure in which the cross section is shaped like the letter V, a so-called V groove, is used in many cases (See reference 3). The reference 3 discloses an optical waveguide substrate in which the V groove is used as the optical fiber holding groove to connect the optical waveguide and optical fiber. By this optical waveguide substrate, since the V groove and the optical waveguide are integrated on a single substrate, efficient connection can be provided even in the case of connection of the optical waveguide with a single mode optical fiber, which requires more accuracy than a connection with a multimode optical fiber.
However, to practically provide such an optical waveguide part, it is necessary that a so-called pigtail type package, in which the optical fiber is arranged at the optical waveguide, be realized. To realize this, the optical fiber is required to be mounted on the V groove with high accuracy. Therefore, conventionally, while observing the optical fiber and the edge surface of the optical waveguide by using an aligning apparatus equipped with a microscope or the like, the optical fiber is arranged on the V groove with the aligning of the optical fiber along the x direction, the y direction, and the z direction on a precise positioning stage or the like. Then, by arranging a glass block or the like on the optical fiber and pressing the glass block, final alignment along the x direction and the y direction is performed. Subsequently, by adhering and fixing it, the optical fiber is mounted. In this way, in the case in which the conventional optical fiber pigtail module is produced, means for aligning the optical fiber by a apparatus such as the precise positioning stage can be employed; however, since the apparatus is too large, it becomes difficult to realize easy optical connecting structure at an actual site at which the optical fiber is laid.
To solve such a problem, much effort has been expended trying to mount the optical fiber on the V groove accurately and easily at low cost. For example, a package including a lower part of the package, an upper part of the package, and a groove for aligning the optical fiber, wherein the optical fiber aligned on the groove for aligning the optical fiber is pressed downwardly by a pressing part arranged on the upper part of the package, is disclosed (See reference 4). In the reference 4, a structure in which an optical waveguide substrate including the groove for aligning the optical fiber such as a V groove arranged on the lower part of the package and the pressing part arranged on the upper part of the package are engaged to press the optical fiber to the V groove and therefore to complete optical connection of the optical waveguide and the optical fiber, is disclosed. By this structure, a part such as glass block or a device such as precise positioning stage can be omitted, and therefore the optical connecting structure may be realized at arbitrarily selected environments in the field of laying optical fiber by improving the workability during aligning of the optical fiber.
However, in the structure according to the reference 4, when the optical fiber is arranged on the V groove before the upper part and the lower part of the package are engaged, alignment along the z direction may be insufficient. That is, there may be a case in which the top of the optical fiber is too far from the edge surface of the optical waveguide, a case in which the optical fiber is too close to the optical waveguide and the fiber rides on the waveguide to break the top or the edge surface thereof, or a case in which the position of the top of the optical fiber is out of alignment.
Furthermore, an optical connecting structure in which the optical connecting position along the axial direction of the optical fiber can be appropriately settled by using an optical fiber holding groove having a structure of which the optical fiber contacts therewith to align the fiber, is disclosed (See reference 5). However, in the optical connecting structure disclosed in the reference 5, since an object of the invention of the reference is to connect an optical fiber and another optical fiber, a position at which the optical fibers contact with each other may be decided relatively, and the position of contact of the fibers may be uncertain against the package.
On the other hand, in many kinds of optical connecting structure, many techniques in which optical fibers are connected with each other as a so-called optical connector, conventionally have been disclosed and used practically. Such an optical connector usually has a structure in which an optical fiber are inserted into an accurate cylindrical element, a so-called ferrule, to be fixed, the ferrule is put in a housing or the like, and such housings are aligned and engaged with each other so that the ferrules therein are faced to each other.
Furthermore, some structures are suggested as an optical connector to connect an optical fiber and a semiconductor device such as an optical waveguide device, a light emitting device, and a light receiving device (See reference 6). To utilize a mechanism for aligning ferrules with each other in the optical connector disclosed in the reference 6, a housing in which an optical element is aligned beforehand and fixed to am opposite side of a connection edge surface of an optical fiber having a ferrule as the optical connector, is prepared, to apply the engaging structure of the optical connector of the optical fiber with each other as a similar engaging structure of the optical fiber and the semiconductor device. In addition, as a purpose for helping the function of aligning of the ferrules with each other, by forming a guide pin and a guide pin hole, respectively, on the housing of the optical fiber connector and the housing of the optical element connector, a structure in which accurate final optical connection can be realized by the two-steps aligning mechanism, is anticipated.
However, such a structure requires an accurate and expensive ferrule, and also requires accurate processing or attaching of the guide pin and guide pinhole on the housing. In addition, since a structure engaging housings with each other and a structure containing various kinds of parts are required, it is necessary that a housing having complicated structure be molded. Therefore, in the overall optical connecting structure, not only is the cost high, but also the overall optical connecting structure is large.
Furthermore, a structure in which a containing structure with a guide pin, guide pin hole, and housing is utilized without using a ferrule, is suggested (See reference 7). Since the structure of the housing in the reference 7 is relatively simple, it is anticipated that production costs can be reduced.
However, the structure of the reference 7 is a structure in which merely the containing structure with the guide pin, guide pin hole, and housing is utilized, and in which an aligning mechanism by an accurate part ferrule is not employed. Therefore, although it can be applied to a plastic optical fiber or a multimode optical fiber having a large core diameter, there may be a problem of variation of connecting loss caused by an insufficient aligning accuracy in the case of butt coupling with a single mode optical fiber or single mode optical waveguide device requiring highly accurate aligning, with a lens requiring highly accurate adjustment of an optical axis, and with a light emitting device such as a laser diode requiring highly accurate aligning.
As a method of realizing such highly accurate aligning, a method using an optical fiber in which a resin coating portion of a common quartz fiber is removed, a so-called bare fiber, and an optical fiber holding groove such as a highly accurately processed V groove, is disclosed (See references 8 and 9). In this case, while pressing the optical fiber from a vertical direction of the optical axis of the optical fiber to the bottom of the V groove, the optical fiber is moved to the bottom direction of the V groove along a side surface of the V shape groove, and the optical fiber is aligned at a predetermined aligning position. Therefore, highly accurate aligning can be finally accomplished even in the case in which the aligning is started from a roughly accurate position of the optical fiber depending on an opening width of the V groove. In this method, the aligning of the vertical direction, that is, the x direction and y direction of the optical axis of the optical fiber is realized at the same time.
In reference 8, a construction of an optical module in which an arc shape groove and a V groove are formed, respectively, on a housing for an optical fiber, called an optical fiber holder and a housing for an optical element called a receptacle, and an optical housing is clipped by these housings from a vertical direction of the axis thereof to accomplish aligning along the x direction and y direction, is disclosed.
Furthermore, in reference 9, a method for connecting an optical module and an optical fiber in which the optical fiber is arranged in advance on a supporting block, a V groove is aligned in advance at an edge surface of an optical waveguide is prepared on the other hand, and this complex of a V groove and an optical waveguide is attached on the optical fiber from a vertical direction of the axis of the optical fiber so that the optical fiber comes into contact with the V groove, to accomplish the aligning of the x direction and y direction, is disclosed.
In these methods for aligning the optical fiber utilizing accurate V groove, although aligning of the vertical direction, that is, the x direction and the y direction of the optical axis of the optical fiber is accomplished at the same time; however, regarding an optical connecting of the axial direction, that is, the z direction of the optical fiber, it is necessary that the length of the optical fiber in the longitudinal direction be prepared in advance at high accuracy to realize highly accurate aligning. For example, in the references 8 and 9, to realize the high accuracy mentioned above, both the optical fiber side and the optical element side are fixed to appropriate housings. Therefore, there may be a problem that highly accurate processing of housing is required to fix it to the appropriate housing in high accuracy, and as a result, a structure of the housing becomes complicated, the number of constituent parts becomes large, and production cost of the optical connecting structure becomes high in its entirety.
Furthermore, arranging in advance the relationship of positions of the optical element or optical fiber and the housing with high accuracy means that high accurate mounting or assembling is required at this step. In some methods, there may be a case in which not only the number of points of optical connecting and the number of constituent parts become unnecessarily large, but also total connecting loss becomes large. Furthermore, since the V groove which has a structure requiring highly accurate aligning is exposed in atmosphere, small foreign matter or the like may contaminate. In the case in which the extraneous material adheres between the optical fiber and side surface of the V groove, there may be a case in which desired high accuracy cannot be obtained and connecting loss is increased.
In reference 10, a construction employs a clamp mechanism to press a V groove and an optical fiber. In addition, a mechanism which improves accuracy in multiple steps by arranging an optical fiber inlet in addition to high accurate aligning means of a V groove or the like, is disclosed. Furthermore, a method in which an optical fiber is inserted and moved to the axial direction (z direction) while keeping the clamping mechanism so that the clamping force does not reach to an optical fiber by a wedge-shaped opening member, and then pullout and position gap of the optical fiber are prevented by removing the opening member and applying the clamp mechanism, is disclosed. In addition, as an aligning method of a tip of the optical fiber along the z direction in which it is inserted, a method by a stopper structure using a gap interface between a bare fiber and a resin coated part, is disclosed.
In the structure of the reference 10, the optical fiber is inserted so as to be arranged on the V groove in a condition in which the clamp mechanism is open; however, at this time, since aligning of the z direction is performed at the gap of the interface of the bare fiber and the resin coated part, in the case in which the length of the bare fiber part is not processed at high accuracy in advance, the top of the optical fiber may be too far from the edge surface of the optical waveguide if the bare fiber part is short. On the other hand, if the bare fiber part is long, the top of the optical fiber is too close to the edge surface of the optical waveguide, and therefore the fiber may ride on the optical waveguide to break the top surface of the optical fiber or the edge surface of the optical waveguide, or the top of the optical fiber may be out of alignment.
Furthermore, in the case in which the pressing force is completely released when the fiber is inserted, as is disclosed in the reference 8, as is mentioned above, the top of the optical fiber may be moved in an unexpected direction during the insertion of the optical fiber. In particular, if the top of the optical fiber is unexpectedly moved upwardly, the fiber cannot be contained in the optical fiber holding groove, and therefore an appropriate optical connecting structure cannot be realized. Such a problem is unlikely to occur in the case in which optical fibers are mutually connected; however, it is a serious problem in the case in which different kind of structures are connected, that is, the optical fiber and the optical waveguide or the like are highly accurately connected. In addition, in a method in which the optical fiber is inserted along the axial direction, like a case in which one whose depth of V groove is relatively shallow, such as when the V groove integrated type optical waveguide is used, in the case in which an optical connection is made with an optical element such that an upper edge part of the optical fiber is higher than that of the optical waveguide is realized, there is a tendency for the top of the optical fiber to ride on the edge surface of the optical waveguide.
Each reference mentioned above is a Japanese Unexamined Patent Application Publication, numbered as follows.    Reference 1: No. Hei07 (1995)-13038    Reference 2: No. Hei08 (1996)-286073    Reference 3: No. 2001-281479    Reference 4: No. 2006-184752    Reference 5: No. 2005-181737    Reference 6: No. 2000-105322    Reference 7: No. Hei07 (1995)-234335    Reference 8: No. Hei11 (1999)-281851    Reference 9: No. 2002-122751    Reference 10: No. 2000-035526